This invention relates to a photometric apparatus for use in an automatic chemical analyzer and, more particularly, to a photometric apparatus which comprises a cell assembly with a plurality of containers, e.g., cells, arranged in a row and containing samples, the cells being caused to pass across a light path of a photometric section for direct measurement of the samples.
Most of the automatic chemical analyzers recently developed have a photometric apparatus of direct measurement type for determining the chemical properties of a sample contained in a cell by illuminating the cell.
In such a photometric apparatus, a measuring point of a cell containing a sample is designated by the signal generated when the cell passes across a light path in the optical system, and the signals obtained from the light transmitted through the measuring point of the cell are processed for light absorption analysis.
A prior art photometric apparatus will now be described with reference to FIG. 1.
The photometric apparatus shown in FIG. 1 comprises cell assembly 1, photometric section 2, position detecting section 3, drive unit 4 and control circuit 5.
Cell assembly 1 includes a plurality of cells 11A, 11B, . . . which can contain samples and holder 12 holding the cells in a row at a predetermined interval. Holder 12 has windows 12a, 12b, . . . through which cells 11A, 11B, . . . are exposed. Windows 12a, 12b, . . . form a light path in photometric section 2. Holder 12 has reflecting marks 13A, 13B, . . . of aluminum foil, provided on the outer wall at predetermined positions beneath windows 12a, 12b, . . . and in the light paths for cells 11A, 11B, . . . .
Photometric section 2 has light source 14, polychromator 15 and detector 16. Light source 14 and polychromator 15 face each other and set apart a predetermined distance, defining a light path. The light projected from source 14 advances along the light path and is applied to polychromator 15. Polychromator 15 has a diffraction grating and forms the spectrum of the light on detector 16. The spectrum consists of bands of negative first order light, 0th order light, first order light, second order light, and so on. Detector 16 detects these bands and generates signals representing these bands of light. The band of 0th order light is the component of the light, which has not been diffracted by polychromator 15. Generally, the bands of negative first order light and the band of first order light are used in photometrical analysis.
Position detector 3 includes light source 17 and light detector 18. Light source 17 and light detector 18 are disposed such that the detector receives the light projected from light source 17 and reflected by a reflecting mark among reflecting marks 13A, 13B, . . . of cell assembly 1. Detector 18 generates a signal when it receives the light projected from light source 17 and reflected by one of reflecting marks 13A, 13B, . . . .
Drive unit 4 drives cell assembly 1 at a predetermined speed along a truck crossing the light path of photometric section 2. Windows 12a, 12b, . . . are thus successively brought to a position on the light path. Control circuit 5 determines the measuring point of the optical system from the signal supplied from light detector 18, and supplies analyzing unit 6 with the photometric signal provided by detector 16. Analyzing unit 6 effects analysis by processing the photometric signal provided from control circuit 5.
In the above prior art photometric apparatus, reflecting marks 13A, 13B, . . . are formed on the outer wall of the cell assembly at the measuring positions of cells 11A, 11B, . . . . These positions are determined according to the shape of the cells. When cells 11A, 11B, . . . are cylindrical, the positions correspond to the centers of the cells. When the cells are rectangular, the positions correspond to the central portions of the cells. The photometric apparatus can determine the measuring positions by detecting reflecting marks 13A, 13B, . . . by position detecting section 3.
In the automatic chemical analyzer, to obtain accurate results of analysis, the cells must be measured at the same position. Also, when each cell is repeatedly measured to identify the changes in reaction state of the sample, the cell must measured at the same position each time. Otherwise, accurate analysis can not be obtained.
An erroneous positioning of reflecting marks 13A, 13B, . . . , reflecting marks 13A, 13B, . . . , light source 17, or light detector 18, would disable detector 18 to accurately detect the measuring positions of the cells. An inaccurate detection of these positions makes an accurate analysis impossible even if no trouble is found in photometric section 2.
Further, a deviation of the parallelness of reflecting marks 13A, 13B, . . . or contamination of thereof occurs over a long use of the apparatus. This also results in an error in measuring the positions of the cells, making an accurate analysis impossible.
Further, when position detecting section 3 has a trouble, it cannot accurately function, thus making an accurate analysis impossible even if no trouble is found in photometric section 2.